Writing COIN-OR CBC Log File

Question

I'm using COIN-OR's CBC solver to solve some numerical optimization problems. I'm structuring the optimization problem in Python via PuLP.

I've noticed that solvers like GUROBI and CPLEX create log files, but I can't seem to figure out how to get CBC to create a log file (as opposed to printing the optimizer's progress to the screen).

Does anybody know of an option in CBC to set a log file? Re-directing all stdout to a file doesn't work for me, since I'm solving a bunch of problems in parallel and want to keep their log files separate.

Here's an example of how I'm calling the solver. This works great and prints progress to the terminal.

prob.solve(pulp.COIN_CMD(msg=1, options=['DivingVectorlength on','DivingSome on']))

Here's how I think a solution should be structured (though obviously LogFileName isn't a valid CBC option).

prob.solve(pulp.COIN_CMD(msg=1, options=['DivingVectorlength on', 'DivingSome on', 'LogFileName stats.log']))

Any help on this would be greatly appreciated. I've been going through the internet, docs, and the CBC interactive session for hours trying to figure this out.

Answer 1

For a solution requiring only a few lines of code in your script that invokes PuLP and CBC, see the solution by James Vogel (https://github.com/voglster, maybe) at https://groups.google.com/forum/#!topic/pulp-or-discuss/itbmTC7uNCQ, based on os.dup() and os.dup2().

I hope it isn't inappropriate to copy it here to guard against linkrot, but see the original post for line-by-line explanation and some sophisticated things I don't understand from the tempfile package. My own usage is less sophisticated, using an actual permanent filename:

from os import dup, dup2, close
f = open('capture.txt', 'w')
orig_std_out = dup(1)
dup2(f.fileno(), 1)

status = prob.solve (PULP_CBC_CMD(maxSeconds = i_max_sec, fracGap = d_opt_gap, msg=1))  #  CBC time limit and relative optimality gap tolerance
print('Completion code: %d; Solution status: %s; Best obj value found: %s' % (status, LpStatus[prob.status], value(prob.objective)))    

dup2(orig_std_out, 1)
close(orig_std_out)
f.close()

This leaves you with useful information in capture.txt in the current directory.